Infra-red heater

ABSTRACT

An infra-red heat generator having a generally cup-shaped body which has an open front end. A perforated diffuser extends across the body lying in a plane parallel to and spaced from the open front end. The diffuser defines a mixing plenum in the rear of the body behind the diffuser. There is an inlet into the plenum for a combustible gas mixture. The percentage of open area of the diffuser is such that during operation a positive pressure is maintained in the plenum. The diffuser is held in place by a spacer which fits into the open end of the body. A multi-layer primary screen lies across the open end of the body. The layers of the primary screen are welded to each other in an orientation with the elements of each layer overlying, in part, the openings of the adjacent layer and the layers are contiguous throughout. The edges of the primary screen lie against the front edges of the generator body which define its open end and the center of the primary screen is convex relative to its edges. The elements of the screen layers are deformed against each other at their crossing points to provide substantial areas of surface contact therebetween. A centrally convex reverberator grid is positioned in front of the primary screen by a spacer that extends between the edges of the screen and the grid. The diffuser, primary screen, grid and spacer are all held in position by a cap which has an inwardly directed lip overlying the edges of the grid and a main flange which telescopes over the front of the generator body and extends around the edges of the primary screen. A retainer is wedged between the outer surface of the body and the main flange of the cap to hold the parts in assembled position.

n States [1 1 [11] 3,8 Placek Dec. 3, 1974 [5 lNFRA-RED HEATER plenumfor a combustible gas mixture. The percentage [75] Inventor: Eugene W.Placek, Middleburg open of the diffu.ser i i during opera- Heights Ohiotron a positive pressure is malntamed m the plenum. The diffuser is heldin place by a spacer which fits into [73] Assignee: International MagnaCorporation, th open end of the body. A multi-layer primary Cleveland,Ohio screen lies across the open end of the body. The layers [22] Filed:Sept. 28, 1973 of the primary screen are welded to each other in anorientation with the elements of each layer overlying, PP 401,837 inpart, the openings of the adjacent layer and the layers are contiguousthroughout-The edges of the primary screen lie against the front edgesof the generaof [58] Field of Search 431/329, 328; 126/92 B the mi ls tW. tPF YEFQ flifi ae 9 elements of the screen layers are deformedagainst [56] References Cited each olther at tli eir :trossing pointsIto ptrovide sub;

stantia areas 0 su ace contact t ere etween. UNITED STATES PATENTScentrally convex reverberator grid is positioned in 3,129,749 4/l964Honger 43l/329 Primary ExaminerCarroll B. Dority, Jr. Attorney, Agent,or Firml-lenry K. Leonard 5 7 ABSTRACT An infra-red heat generatorhaving a generally cupshaped body which has an open front end. Aperforated diffuser extends across the body lying in a plane parallel toandspacedfrom the open front end. The diffuser defines a mixing plenumin the rear of the body behind the diffuser. There is an inlet into thefront of the primary screen by a spacer that extends between the edgesof thescreen and the grid. The diffuser, primary screen, grid and spacerare all held in position by a cap which has an inwardly directed lipoverlying the edges of the grid and a main flange which telescopes overthe front of the generator body and extends around the edges of .theprimary screen. A retainer is wedged between the 9 Claims, 10 DrawingFigures PATENIELBEB 31914 I .SIEEI 20F 2 ifi- 15 INFRA-RED HEATERBACKGROUND OF THE INVENTION Portable, gas-fired radiant heat generatorsusually are designed for assembly onto pressurized containers of propaneor butane gas. Such heaters, for the most part, have been unnecessarilycomplex, both in manufacturing and assembly, and have embodied designfaults which necessitated the utilization of expensive heat resistantgaskets, assembly means such as screws, nuts, bolts, clips, and thelike, and frequently have been so poorly designed as to requireextremely careful handling in order to prevent flashbacks of the burninggasesand the loss of efficiency.

It is, therefore, the principal object of the instant invention toprovide a gas-fired infra-red heat generator which consists of a smallnumber of parts, each simple to manufacture, and that is so designed asto provide for simplicity of assembly and consequent lightweight and lowcost.

It is another object of the instant invention to provide a gas-firedinfra-red heat generator not only so designed to reduce its cost bysimplifying its assembly and the number of parts involved, but also toincorporate design considerations by which the possibility of flashbackis substantially eliminated, by which the transfer of heat produced iscontrolled to improve its efficiency and yet which is lightweight,inexpensive to manufacture and effective for the purpose designed.

It is yet anotherobject of the instant invention to provide a small,lightweight infra-red heat generator which is particularly adapted foruse in the removal of paint, the softening of adhesives such as thoseused to fix vinyl or asphalt floor tiles and the softening of such tilesthemselves to facilitate their laying and/or removal.

Another important object of the instant invention is to provide aportable infra-red heat generator which is simple to assemble but whichsubstantially precludes dis-assembly by an ordinary user thus tosubstantially eliminate the problems which would result upon improperre-assembly of the generator by a non-trained person.

A still further object of the instant invention is to provide aninfra-red heat generator having a superior primary or combustion screenso designed as to substantially eliminate flashback, to achieveradiation temperatures rapidly, to reach and remain at substantiallyuniform temperature throughout its over-all area and to enable thegenerator to operate-efficiently in almost any position.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical sectional view ofa generator embodying the invention;

FIG. 2 is a view in front elevation taken at the right side of FIG. 1,with parts broken away;

FIG. 3 is a vertical sectional view taken along line 3--3 of FIG. 1;

FIG. 4 is a vertical sectional view taken along line 4-4 of FIG. 1; 1

FIG. 5 is an isometric view of the primary screen employed in'agenerator according to the invention; FIG. 6 is a fragmentary view,partly in section and partly in elevation, illustrating a modificationof the assembly means of a generator embodying the invention;

FIG. 10 is a comparative view on a greatly enlarged scale of fragmentsof screen elements at their crossing points as in an old screen and asin a screen shaped according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A radiant heat generatorembodying the invention has a generally cup-shaped body indicated by thereference number 10 which has an open front end. An inlet pipe 11 for amixture of combustible gases is connected to the rear portion of thebody 10. The pipe 11 comprises an air induction venturi (not shown) andis connected to a pressurized gas container. Gas from the container isfed through the venturi by which air is inspirated with the gas and thenthe combustible mixture flows through the inlet pipe 11 into a chargingplenum l2 defined by the rear and walls of the body 10 and a diffuserI3.

The perforated diffuser 13 extends across thebody l0 and is held inplace by a spacer 14 which fits within the open end of the body 10. Inthis embodiment of the invention the spacer 1-4 is a separate piece,being formed as a split-ring which holds the diffuser at a fixeddistance from the edge of the body '10 which defines its open end 13. Ina generator according to the invention the diffuser 13 has a percentageof open area selected to control the rate of flow of the combustiblemixture through the perforations from the plenum l2 forwardly at a ratesuch that a positive pressure is maintained in the plenum 12 and thatthe flow rate of the gases through the perforations will be in excess ofthe flame propagation speed of the gases to be combusted thus to aid inthe substantial elimination of flashback of the burning gases into thechamber 12.

Contrary to the teachings of some prior art workers, 1 have found thatfor infra-red heat generators to be employed with butane and propanegases from regulated pressurized containers, the percentage of open areain the diffuser should not be above 30 percent nor below 10 percent andpreferably should be in the order of 20-25 percent. In a generatoraccording to the invention, operating on liquified gas, optimumoperation is achieved with an open area of 23 percent.

The front edge of the spacer l4 lies substantially in the same plane asthe front circular end of the walls of the body 10 and preferably isfabricated from at least slightly resilient material so that it can beeasily inserted into the open end of the body 10, and, upon expansion,will frictionally engage the inner surface of the wall of the body 10,securely retaining the diffuser plate 13 in place.

A convexly crowned, multi-layer, primary screen 15 consisting of atleast two layers of screening 15a and 15b has a size such that its edgeoverlies the edge or end of the body 10 and may extend outwardlyslightly beyond the edge of the body 10. The two layers of screen 15aand l5b'preferably are shifted relative to each other so that the screenelements of each layer overlie in part the openings between the elementsof the other layer, as is shown in FIG. 9. Such overlapping creates atortuous path for the passage of gas through the two layers of thescreen 15. The two layers a and 15b are welded together, as indicated bythe reference number 16, to maintain them in the overlapped orientationand to hold them contiguous to each other throughout their surfaces.After the two layers 15a and 15b are oriented as described and weldedtogether, they are convexly crowned in a pair of coining dies which areclosed to such spacing that the individual screen elements, i.e., thewires, are deformed against each other to greatly increase their contactthroughout their surfaces. As can be seen by comparing the two parts ofFIG. 10, an ordinary screen, (indicated by the legend Old) has pointcontact only between the surfaces of its crossing wires 17 and 18. Insharp contrast, when the screens 15a and 15b are coined, the individualelements or wires are deformed so that each contact between touchingwires 19 and 20 becomes a surface 21. The resulting tremendous increasein surface contact between the elements of each layer 15a or 15b and,similarly, between the elements of layer 15a and those of 15b, providesfor rapid and uniform heat transfer between the screen layers 15a and15b. In one embodiment of the invention, for example, each layer has anominal thickness of .040 inch and the two layers are coined to acombined thickness of .060 .065 inch.

The convex crowning of the screen 15 is also accomplished at the time ofcoining and establishes a bias forwardly so that as the screen 15expands upon increase in its temperature, it cannot bow in a concavedirection, thus preventing it from decreasing the space in front of thediffuser plate 13 and eliminating any possibility that it might evencontact the diffuser plate 13.

The exposure of the elements of the inner screen layer 15b between theelements of the forward layer 150, resulting from the staggeredorientation illustrated in FIG. 9, has the added advantage of increasingthe area of the screen 15 which is visibly exposed when raised toinfra-red generating temperature.

A second spacer 22 lies against the edges of the screen 15 and extendsforwardly to space and position a reverberator grid 23 that isfabricated from an open mesh screen and which is also crowned in itscentral portion on a curvature approximately the same as that of thecoined screen 15. Preferably the grid 23 also is coined to deform itselements against each other in order to create surfaces of contactbetween them, as illustrated in FIG. 10. The edges of the grid 23overlie the spacer 22.

The entire assembly so far described is retained on and in the end ofthe body 10 by a cap 24. The cap 24 has an inwardly directed lip 25 anda backwardly extending flange 26. The lip 25 has an open diametersubstantially equal to the inside diameter of the spacer 22 and overliesand is positioned against the edge of the reverberator grid 23. Theflange 26 has an inside diameter in which the spacer 22 makes arelatively tight friction fit and it is large enough to extendbackwardly circumjacent the edge of the body 10 toward the rear of thebody 10. The diameter of the flange 26 of the cap 24 is such that anannular space remains between the inner side of the flange 26 and theouter surface of the front portion of the body 10. In the embodiment ofthe invention illustrated in FIGS. 1-5, inclusive, with particularreference to FIG. 1, an annular locking ring 27 is wedged in thisannular space between the flange 26 and the outer surface of the body10.

In assembling a heater as described above, the diffuser plate 13 isdropped into the open end of the body 10 and the first spacer 14 is thenforced in to hold the diffuser plate 14 in place. The reverberator grid23 is then put into the open cap 24, lying against its lip 25 and thesecond spacer 22 then forced into the cap 24 to retain the edge of thegrid 23 against the inner side of the lip 25. The primary screen 15 isthen positioned against the edge of the body 10 and the edge surface ofthe spacer l4, and the cap 24 (with the spacer 22 and reverberator grid23) is telescoped over the open end of the body 10. The locking ring 27is thenwedged forwardly from the back to tightly retain the elements inassembled position.

FIG. 6 shows a modified structure for assembling a generator embodyingthe invention in which a wire-like locking ring 28 is used instead ofthe annular, flat, locking ring 27 shown in FIG. 1. After assembling thediffuser 13, spacer 14, and screen 15 in the body 10 and the grid 22 inthe cap 24, the cap 24 is telescoped over the body 10, as describedabove. The wire locking ring 28 is then forced into the annular spacebetween the flange 26 of the cap 24. The flange 26 is staked at severalpoints around its periphery, for examples, as indicated by the referencenumbers 29. The staking retains the locking ring 28 in place and,therefore, fixes the entire assembly as illustrated in FIG. 6, in apermanent manner.

In the embodiment of the invention illustrated in FIGS. 7 and 8 agenerator according to the invention comprises an open ended body 30 towhich a combustible mixture of gas and air is fed from an inlet pipe 31.The inlet pipe 31 leads into the side of the body 10 and the rearportion of the body 10 functions as a plenum 32, the forward margin ofwhich is defined by a transversely extending diffuser 33. In thisembodiment of the invention the diffuser 33 and its spacer are integral,a circular flange 34 of the diffuser 33 serving to space its main webrearwardly of the open end of the body 30. The spacer flange 34 of thediffuser 33 has an outwardly directed lip 34a which fits against theforward edge of the body 10 defining its open end. The spacer flange 34of this embodiment of the invention functions identically with the firstspacer ring 14 of the embodiments illustrated in FIGS. 1-5 and 6.

As in the earlier described embodiments of the invention a multi-layerprimary screen 35, identical with the screen 15 of the earlierembodiments, is positioned across the open end of the body 10 and,similarly, two layers 35a and 35b of the screen 35 are retained in theirproperly oriented and contiguous relationship (as described above) by acenter weld 36. A second spacer 37 and a reverberator grid 38 arepositioned on the open end of the body 10 by a lipped cap 39 and alocking ring 40 similar to those of the earlier described embodiments.

FIG. 7 also illustrates the utilization of a reflector 41 designed toconcentrate and, to a certain extent, to focus, the infra-red energyemitted from the primary screen 35 and the reverberator 38. Thereflector 41 has a flared section 42 and a circular rim 43 which fitsclosely circumjacent the outer surface of the retainer cap 39. Thereflector 41 is permanently mounted on the generator by the use of aplurality of inwardly extending drive pins 44 which extend through thecircular rim 43 of the reflector 41 and through the cap 39 into thelocking ring 40.

Thus, although the wedging of the locking ring 40 into the positionillustrated permanently assembles the elements of the generator againstready dis-assembly, the drive pins 44 which mount the reflector 41render dis-assembly of the parts even more difficult.

A generator according to the invention, as illustrated in FIG. 7operating with regulated entry pressure of the air/gas mixture and aratio of approximately 10 parts of air to one part of propane, has beenfound to be extremely effective as a hand held tool for the purpose ofsoftening paint to expedite its removal, softening adhesives whichretain vinyl and asphalt floor tiles, and the like, and softening thetiles themselves in order to facilitate their cutting and placement. Thetemperature of the front layer a of the primary screen 15 quicklyreaches the level of about 1,600 F while the inner layer 15b of thescreen remains below l,000 F due to the cooling effect of the gaseousmixture flowing through the fuel diffuser 13 and thence through thelayers of the primary screen 15. It is believed that these temperaturesare reached and maintained by reason of the direct metal to metalcontact between the edges of the screen 15 and the spacers 14 or 34, thespacers 22 and 37 and the reverberator grids l7 and 38. Under theseconditions the reverberator grid also reaches and remains at atemperature of l,600 F.

Contrary to previous teachings such as those in Honger US. Pat. Nos.3,021,893 and 3,129,749, 1 have found that the intimate contactthroughout their surfaces of the two layers 15a and 15b of the primaryscreen 15, particularly when deformed to provide surfaces for heattransfer as illustrated in FIG. 10, results in a more nearly perfectlyuniform operating temperature across the outer faces of the overlappedprimary screen layers 15a and 15b and yet establishes the substantialtemperature differential between the inner screen layer 15b and thefront screen layer 15a. I believe that this results from the transfer ofheat from the inner screen layer 15b to the mixture of air and fueldelivered to the space behind the primary screen layer 15b through theapertures in the diffuser 13 or 33.

Substantial elimination of all tendency of a generator embodying theinvention to flashback" is believed to result from the establishment ofthree different pressure zones. The pressure in the plenum behind thediffuser plate 13 or 33 is substantially higher than the pressure in thezone in front of the diffuser plate 13 or 33 between it and the primaryscreen 15, by reason of the restrictions of the orificesin the diffuser13 or 33. Because the air/gas mixture then flows through the tortuouspassagesbetween the elements of the primary screen layers as illustratedin FIG. 9, the third pressure zone in front of the screen 15 in the areainto which the gasses are combusted is lower than the pressure in thespace between the diffuser 13 or 33 and its respective screen 15.Combustion of the gases actually takes place in the interstices betweenthe elements of the two screen layers 15a and 15b andthe outer 180cylindrical surfaces of the screen elements rapidly reach infraredemitting temperature so that they generate and direct the maximum amountof free radiant energy at the 6 reverberator grid. The reverberator gridreaches operating temperature in a very short span of time, say in theorder of a few seconds.

The edge surfaces of both the reverberator grid and the primary screenwhich are in contact with the spacer and the body deliver a portion ofthe heat energy to the body 10 and, therefore, to the diffuser 13 or 33and that heat is in turn absorbed to a large degree by the incoming coldcombustible gases which flow through the perforations of the diffuser 13or 33. This results in heating and expanding the incoming combustiblegases and cooling the surfaces of the generator body 10.

In the embodiment of the invention illustrated in FIG. 7, heattransferred to the spacer from the reverberator grid and primary screenalso is transferred to the rim and the conical section of the reflectorwhence it is radiated into the area around the reflector which furthercools the body 10.

An additional desirable aspect of a generator embodying the inventionresults from the fact that no positive mounting means such as pins,bolts, screws, or rivets are necessary to fix the position of .the edgesof the primary screens 15 or the reverberator grids 23 or 38. Thus,particularly because both of them are crowned forwardly as describedabove, as they expand upon in crease in their temperatures, there is notendency for either to be buckled or malformed. Not only is the centerportion free to move forwardly as it increases in temperature andexpands but also the edges are not prevented from moving outwardly as aresult of expansion under high temperature.

What I claim is:

1. A gas-fired infra-red heat generator comprising, in combination,

an open-ended, cup-shaped body defining a plenum,

a combustible fuel mixture inlet into said plenum,

a perforated diffuser extending across said body and defining the frontmargin of said plenum,

a first spacer fitting within the open end of said body for holding saiddiffuser in position,

a primary screen having interwoven metal elements, said primary screenextending across the open end of said body and having a size slightlylarger than and extending outwardly beyond the end of said body, saidprimary screen being crowned convex in its central area,

a second spacer having an inner diameter substantially equal to the openend of said body and positioned against the margin of said primaryscreen,

a reverberator grid of substantially the same diameter as the outerdiameter of said second spacer,

the margins of said grid and said primary screen being in direct contactwith opposite sides of said second spacer,

a cap having an inwardly directed lip engaging the margin of said gridand a perimeter flange extending around and beyond said second spacerand spaced from the outer surface of said body,

and a means comprising a locking ring positioned between the innersurface of said cap wall and the outer surface of said body for holdingsaid cap on said body and said diffuser screen, grid and spacers inassembled relationship.

2. A generator according to claim 1 in which the first spacer is anannular flange integral with the diffuser.

3. A generator according to claim 1 in which the interwoven elements ofthe primary screen are deformed at their crossing points forestablishing surface contacts between the elements.

4. A generator according to claim 1 in which theprimary screen has atleast two layers that are contiguous throughout their surfaces.

5. A generator according to claim 4 in which the elements of each layerof said screen overlap the interstices of an adjacent layer.

6. A generator according to claim 1 in which the diffuser has an openarea in the range of more than percent and less than 30 percent.

7. A generator according to claim 6 in which the open area of thediffuser is in the range of to percent.

8. A generator according to claim 1 having a flared reflector whichcomprises a flange fitting closely circumjacent the flange of the capand is secured thereto.

lishing surface contacts between the elements.

1. A gas-fired infra-red heat generator comprising, in combination, anopen-ended, cup-shaped body defining a plenum, a combustible fuelmixture inlet into said plenum, a perforated diffuser extending acrosssaid body and defining the front margin of said plenum, a first spacerfitting within the open end of said body for holding said diffuser inposition, a primary screen having interwoven metal elements, saidprimary screen extending across the open end of said body and having asize slightly larger than and extending outwardly beyond the end of saidbody, said primary screen being crowned convex in its central area, asecond spacer having an inner diameter substantially equal to the openend of said body and positioned against the margin of said primaryscreen, a reverberator grid of substantially the same diameter as theouter diameter of said second spacer, the margins of said grid and saidprimary screen being in direct contact with opposite sides of saidsecond spacer, a cap having an inwardly directed lip engaging the marginof said grid and a perimeter flange extending around and beyond saidsecond spacer and spaced from the outer surface of said body, and ameans comprising a locking ring positioned between the inner surface ofsaid cap wall and the outer surface of said body for holding said cap onsaid body and said diffuser screen, grid and spacers in assembledrelationship.
 2. A generator according to claim 1 in which the firstspacer is an annular flange integral with the diffuser.
 3. A generatoraccording to claim 1 in which the interwoven elements of the primaryscreen are deformed at their crossing points for establishing surfacecontacts between the elements.
 4. A generator according to claim 1 inwhich the primary screen has at least two layers that are contiguousthroughout their surfaces.
 5. A generator according to claim 4 in whichthe elements of each layer of said screen overlap the interstices of anadjacent layer.
 6. A generator according to claim 1 in which thediffuser has an open area in the range of more than 10 percent and lessthan 30 percent.
 7. A generator according to claim 6 in which the openarea of the diffuser is in the range of 20 to 25 percent.
 8. A generatoraccording to claim 1 having a flared reflector which comprises a flangefitting closely circumjacent the flange of the cap and is securedthereto.
 9. A generator according to claim 1 in which the reverberatorgrid is a woven metal mesh and the elements thereof are deformed attheir crossing points for establishing surface contacts between theelements.